[Android]Android字体高度的研究
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android自定义View绘制的时候,会有很多情况下要与字体打交道,涉及到字体宽度、高度的时候要特别注意一下几个概念,见图:
baseLine:一行文字的底线。
Ascent: 字符顶部到baseLine的距离。
Descent: 字符底部到baseLine的距离。
Leading: 字符行间距。
- public class TestOnDraw extends Activity {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- // TODO Auto-generated method stub
- super.onCreate(savedInstanceState);
- MyView v = new MyView(this);
- this.setContentView(v);
- }
- }
- class MyView extends View
- {
- public MyView(Context context) {
- super(context);
- }
- @Override
- protected void onDraw(Canvas canvas) {
- super.onDraw(canvas);
- Paint p = new Paint();
- p.setColor(Color.WHITE);
- p.setTextSize(50);
- p.setAntiAlias(true);
- FontMetrics fm = p.getFontMetrics();
- System.out.println("top = "+ fm.top);
- System.out.println("ascent = "+ fm.ascent);
- System.out.println("descent = "+ fm.descent);
- System.out.println("bottom = "+ fm.bottom);
- System.out.println("leading = "+ fm.leading);
- int textHeight = (int) (Math.ceil(fm.descent - fm.ascent) + 2);
- System.out.println("textHeight = " + textHeight);
- float width =500;
- float baseline = 100f;
- float offsetAscent = baseline + fm.ascent;
- float offsetDescent = baseline +fm.descent;
- float offsetTop = baseline + fm.top;
- float offsetBottom = baseline + fm.bottom;
- canvas.drawText("中国 bp Android", 0, baseline, p);
- canvas.drawLine(0, baseline, width, baseline, p);//baseline
- canvas.drawLine(0, offsetAscent, width, offsetAscent, p);//ascent
- canvas.drawLine(0, offsetDescent, width, offsetDescent, p);//descent
- canvas.drawLine(0, offsetTop, width, offsetTop, p);//top
- canvas.drawLine(0, offsetBotton, width, offsetBottom, p);//bottom
- }
- }
- public class TestOnDraw extends Activity {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- // TODO Auto-generated method stub
- super.onCreate(savedInstanceState);
- MyView v = new MyView(this);
- this.setContentView(v);
- }
- }
- class MyView extends View
- {
- public MyView(Context context) {
- super(context);
- }
- @Override
- protected void onDraw(Canvas canvas) {
- super.onDraw(canvas);
- Paint p = new Paint();
- p.setColor(Color.WHITE);
- p.setTextSize(50);
- p.setAntiAlias(true);
- FontMetrics fm = p.getFontMetrics();
- System.out.println("top = "+ fm.top);
- System.out.println("ascent = "+ fm.ascent);
- System.out.println("descent = "+ fm.descent);
- System.out.println("bottom = "+ fm.bottom);
- System.out.println("leading = "+ fm.leading);
- int textHeight = (int) (Math.ceil(fm.descent - fm.ascent) + 2);
- System.out.println("textHeight = " + textHeight);
- float width =500;
- float baseline = 100f;
- float offsetAscent = baseline + fm.ascent;
- float offsetDescent = baseline +fm.descent;
- float offsetTop = baseline + fm.top;
- float offsetBottom = baseline + fm.bottom;
- canvas.drawText("中国 bp Android", 0, baseline, p);
- canvas.drawLine(0, baseline, width, baseline, p);//baseline
- canvas.drawLine(0, offsetAscent, width, offsetAscent, p);//ascent
- canvas.drawLine(0, offsetDescent, width, offsetDescent, p);//descent
- canvas.drawLine(0, offsetTop, width, offsetTop, p);//top
- canvas.drawLine(0, offsetBotton, width, offsetBottom, p);//bottom
- }
- }
运行效果:
这是程序的输出结果:
得出结论: canvas drawText() 的startX是从左下角的baseline的底线开始绘画的,如果我们要得到字体的高度需要关注descent - ascent (ascent线在baseline上面,所以是负数)
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